This invention relates to circuit breaker assemblies with a thermal trip unit and, more particularly, to circuit breakers with an adjustable thermal trip unit.
Circuit breakers typically provide protection against persistent overcurrent conditions. This type of protection is provided in many circuit breakers by a thermal trip unit, which trips the circuit breaker""s operating mechanism to open the circuit breaker""s main current-carrying contacts on persistent overcurrent conditions.
Modem thermal trip units include a bimetallic strip (bimetal) that bends at a predetermined temperature. One end of the bimetal is attached, typically with a screw, to a strap that conducts current from the power source to the protected circuit. Another end of the bimetal is adjacent a trip bar. Upon the occurrence of an overcurrent condition, the bimetal bends towards the trip bar and contacts the trip bar which is mechanically linked to the operating mechanism causing the main current-carrying contacts to open and stop the flow of electrical current to a protected circuit.
It is necessary for such thermal trip units to be reliable. In addition, it is desirable that thermal trip units can be adjusted or calibrated so that the breaker can be adjusted to trip at different levels of overcurrent. Typically, after a circuit breaker is assembled, each pole of the breaker is then calibrated to trip at a predefined level by adjusting corresponding calibration screws. If the circuit breaker cannot be properly calibrated due to any misalignment of the calibration screws that occurred during assembly, the breaker must be disassembled and then reassembled. Disassembly and reassembly of the circuit breaker significantly decreases the calibration yield and increases production costs. Proper alignment of the calibration screws is particularly important in a multi-pole circuit breaker since each pole""s calibration screw must be aligned. The misalignment of any one calibration screw mandates the disassembly and reassembly of the circuit breaker.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by the present invention.
In an exemplary embodiment of the invention, a molded circuit breaker cover for providing access to a calibration screw of a thermal trip unit includes an exterior surface having an opening disposed therein and a locator extending from an underside of the cover. The locator includes a channel surface defining a channel continuous with the opening wherein the locator captures the calibration screw and aligns the calibration screw with the opening.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following figures and detailed description.